Rearrangement of bromofluorinated propene

ABSTRACT

THE NEW COMPOUND PERFLOURO(METHALACETYLENE) IS PREPARED BY A SERIES OF REACTIONS INVOLVING THE NEW INTERMEDIATE COMPOUNDS 3-BROMO-1,1,3,3-TETRAFLUOROPROPENE; 1,2,3TRIBROMO-1,1,3,3-TETRAFLUOROPROPANE; 2,3-DIBROMO-1,1,3,3TETRAFLUOROPROPENE; AND 1,2-DIBROMO-1,3,3,3-TETRAFLUOROPROPENE.

United States Patent 3,709,948- REARRANGEMENT 0F BROMOFLUORINATED PROPENE Robert Neville Haszeldine, Disley, Ronald Eric Banks,

Torkington, and David Robin Taylor, Bramhall, England (all Pennwalt Corporation, 900 1st Ave., King of Prussia, Pa. 19406) No Drawing. Filed June 26, 1969, Ser. No. 836,948 Claims priority, application Great Britain, July 12, 1968, 33,407/ 68 Int. Cl. C07c 21/18 US. Cl. 260653.3 1 Claim ABSTRACT OF THE DISCLOSURE The new compound perfiuoro(methylacetylene) is prepared by a series of reactions involving the new intermediate compounds 3-bromo-1,1,3,3-tetrafiuoropropene; 1,2,3 tribromo-l,1,3,3-tetrafiuoropropane; 2,3-dibromo 1,l,3,3 tetrafluoropropene; and 1,2 dibromo-1,3,3,3-tetrafluoropropene.

This invention is concerned with the novel compound perfiuoro (methylacetylene), a method for its preparation, and the novel intermediates formed in its preparation. According to this method, dibromodifluoromethane is reacted with 1,1-difluoroethylene, for example, at an elevated temperature and in the presence of an organic peroxide, such as benzoyl peroxide, to give 1,3 dibromo-1,1,3,3-tetrafluoropropane. Dehydrobromination of this compound gives 3-bromo-1,1,3,3-tetrafiuoropropene which is then brominated to give 1,2,3-tribromo-1,l,3,3-tetrafiuoropropane. Dehydrobromination then gives 2,3-dibromo-1,1,3, 3-tetrafluoropropene which is capable of molecular rearrangement to 1,2-dibromo-1,3,3,3-tetrafluoropropene. Debromination then gives perfluoro(methylacetylene) in good yield.

Two noteworthy steps in the above route are the dehydrobromination of 1,3 dibromo-l,1,3,3-tetrafiuoropropane, which may be carried out by heating under reduced pressure in the presence of a mixture of carbon and silica, and the molecular rearrangement of 2,3-dibromo-1,1,3,3- tetrafluoropropene to 1,2 dibromo-1,3,3,-tetrafiuoropropene, which may be carried out at room temperature or below in the presence of aluminum bromide.

The bromination of 3 bromo-l,1,3,3-tetrafiuoropropene may be carried out conventionally by reaction with bromine and the subsequent dehydrobromination by treatment with aqueous potassium hydroxide. The final debromination may be carried out by refluxing 1,2-dibromo- 1,3,3,3-tetrafluoropropene with zinc in the presence of dioxane.

The complete reaction scheme is as follows:

C/SiOz 3,709,948 Patented Jan. 9, 1973 the foregoing intermediates of the formulae:

The method of this invention is clarified by referring to the following example wherein, according to the reaction scheme and conditions set out above, dibromodifluoromethane was reacted with 1,1-difiuoroethylene to give 1,3- dibromo-l,1,3,3-tetrafiuoropropane in 62% yield. Dehydrobromination gave 3-bromo-1,1,3,3-tetrafiuoropr0pene in 86% yield. Bromination gave 1,2,3-tribromo-1,1,3,3- tetrafluoropropene in 92% yield which was dehydrobrominated in 91% yield. The 2,3-dibromo-1,1,3,3-tetrafluoropropene cooled and treated with AlBr underwent molecular rearrangement to give 1,2-dibromo-l,1,3,3-tetrafluoropropene in 97% yield and cisztrans ratio of 60:40. Refiuxing of the cis/trans product with zinc in dioxane gave product perfiuoro(methylacetylene) in 43% yield.

The intermediates and product were identified by elemental analysis and spectroscopic methods. Perfluoro (methylacetylene) is a colorless gas, B.P. 50" C. Infrared spectroscopic analysis shows strong absorption at 4.24 1. and the F n.m.r. spectrum (35/56.46 mc./sec.) shows two absorptions 50.8 (doublet); 5 (quartet) 203.0 IJ I 4.3 c./sec.] with relative intensity 3.1 [for the C satellite of the 5 50.8 doublet !J [=259.0

and |JCCF|=57.7 c./SCC.

(6 =0.011i0.002 p.p.rn.)]

Perfluoro (methylacetylene) undergoes no change when stored in glass at 25/10 cm. Hg for 1 month or at 20/ atm. for 4 days. Perfluoro(methylacetylene) decomposes slowly in water and reacts with potassium fluoride in the presence of formamide to give 1,1,3,3-pentafiuoropropene. Compared with the highly explosive nature of monofiuoroacetylene, perfluoro(methylacetylene) shows surprising stability. Perfluoro (methylacetylene) undergoes copolymerization with various comonomers as shown for its hydrocarbon analogue, propyne, in Belgian Pat. 624,654 and British Pat. 889,730 and 897,099; however, the copolymers having the fiuorinated segments derived from perfluoro(methylacetylene) have considerably greater thermal stability.

We claim:

1. The method of treating 2,3 dibromo 1,1,3,3-tetrafluoropropene with aluminum bromide to produce 1,2-dibromo-l,1,3,3-tetrafiuoropropene by molecular rearrangement thereof.

References Cited UNITED STATES PATENTS 4/1951 Gochenour 260653.3

OTHER REFERENCES DANIEL D. HOROWITZ, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT orrica CERTIFICATE OF CORRECTIQN Patent No. 3, 709, 948 Dated Tanuarv 9. 1973 Inventor(s) Robert Neville Haszeldine, Ronald Brig Banks, [Qayjd Robin Taylor It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F Column 1, line 44 "-l, 3, 3, should read -l, 3, 3, 3, Y

Column 1, line 60 that portion of the formula. reading "COgzCFg should read --CH :CF

Column 1, line 62 that portion of the formula reading "50%KOHag" should read -50%KOHaq-- Column 1, last line that portion of the formula. reading CF C:CP" should read CF C? CF a Column 2, line 18 "1,1, 3, 3-" should read -l, 3, 3,3 Column 2, line 30 that portion of the formula. reading "+13 2 should read -+0. 132 Column 2, Claim 1, line 50 "1,1, 3, 3" should read '-l, 3, 3, 3--

Signed and sealed this 2 2nd day of May 19 73 (SEAL) Attest;

EDWARD M.IFLETCHER,JR. Attesting Officer ROBERT GOTTSCHALK Commissioner of Patents 

